This project continues studies aimed at understanding host immune mechanisms involved in the tumor-host relationship. The models to be examined involve cloned MCA induced murine fibrosarcomas in multiple congenic and/or recombinant lines. These tumors are characterized for TSTA, H2 antigens, and MuLV gp70 representation. More information will be sought on the relation between TSTA and H2 or MuLV antigens on the tumor surface. Through immunogenetic and serologic approaches, analysis of H2 deficient varients, and biochemical dissection of the tumor cell membrane any molecular identities of these elements will be determined. The host responses to tumor bearing will continue to receive scrutiny, in terms of T-cells and T-cell subclasses of known phenotypes, and natural killer cells. Tumor-directed specificity, in vivo as well as in vitro functions as suppressors and killer cells will be delineated. Several techniques developed in this laboratory will be employed in these studies, including TAA specific proliferation assay, adoptive protection assay, an apparently TSTA specific cytotoxicity assay, and a tumor cell membrane tagging method.